1. Field of the Invention
The present invention relates to a mobile device having a disk drive that has a reduced battery drain in performing a track seeking operation when operating in a mobile environment.
2. Description of the Related Art
Hard disk drives store large volumes of data on one or more disks mounted on a spindle assembly. The spindle assembly includes a spindle motor for rotating the disks at a nominal angular velocity. Disk drives employ a disk control system for interfacing with a host (e.g., a computer) to control the reading and writing of data on a disk. Each disk includes up to two disk surfaces which are capable of storing data. On each disk surface, user data is stored in concentric circular tracks between an outside diameter and an inside diameter of the disk. Servo systems are employed to maintain alignment of a transducer head with a desired target data track (termed xe2x80x9ctrack followingxe2x80x9d) for reading and writing user data on the disk surface within desired control parameters.
Embedded servo systems store servo data on the same disk surface as user data to provide control signals and information employed in the operation of the servo system. User data on the disk surface is divided into groups of data sectors. Embedded servo information is recorded in servo sectors placed in arcuate, radially continuous narrow wedges between the groups of data sectors. In this regard, servo sectors are commonly referred to as xe2x80x9cservo wedges.xe2x80x9d For example, a concentric data track may typically include 120 equally spaced servo wedges with data regions (i.e., a region typically containing 3-6 data sectors and up to 2 partial data sectors) located between adjacent pairs of servo wedges.
Each servo wedge includes fields containing track identification used in track seeking operations and tracking information used in track following operations. For example, the track identification information may include track number and/or address and wedge number, and the tracking information may include automatic gain control (AGC) and phase lock oscillator information (PLO), timing information (e.g., a servo sync word) and servo burst information for positioning a transducer head over the disk surface. The fields are defined by transitions written on the disk surface in patterns readable by the servo system. During execution of a command to read or write data to a target data sector on the disk surface, servo information is sampled as the servo wedges pass under the associated transducer head. The rate at which servo information is sampled, termed xe2x80x9cservo sampling rate,xe2x80x9d is therefore determined by the number of wedges per track and the angular velocity of the disk.
Disk drive design engineers strive to optimize designs at a servo sampling rate which enables reliable transducer head positioning by avoiding resonances from actuator mechanics, providing adequate servo system phase margins, and detecting shock events. A further constraint on optimization of servo sampling rate is a tradeoff between angular velocity of the disk and the number of wedges per track. Since the wedges are embedded in the data track, some capacity which could be available for user data is consumed, therefore it is desirable to achieve an efficient surface format by only including a sufficient number of wedges per track necessary to meet the optimum servo sampling rate for a given angular velocity.
The process of moving a head from a current track position to a desired or target track position is known as a xe2x80x9cseek.xe2x80x9d The disk drive includes a servo system that is utilized both to seek to a selected target track and thereafter follow the target track on the disk. A seek to a selected target track is commonly made in accordance with a profile of command effort to the actuator for a respective seek distance, which is stored in memory and accessible by the servo system controller.
The seek profile can be described in terms of current draw, velocity, position or cumulative power consumption. A seek profile (described in terms of velocity) can include three components: an acceleration profile, an optional coast interval, and a deceleration profile. The acceleration profile, typically set to the maximum acceleration permitted by the hardware, involves the initial portion of the seek when the actuator is gaining speed. A coast interval may be included during which the velocity remains substantially constant. The deceleration profile ends with both acceleration and velocity close to zero as the head approaches the target track.
In FIGS. 2-7, exemplary idealized current, cumulative power consumption and velocity seek profiles for two seek operations for a given distance are shown. In FIGS. 2-4, current, cumulative power and velocity profiles graphically illustrate a first seek operation. In FIG. 4, the actuator is commanded to accelerate at time T0. This acceleration is maintained until the velocity of the actuator reaches a peak value VELPK. This occurs at time TSWITCH. The actuator is then commanded to decelerate, until time TEND, at which time the deceleration and velocity are brought back to zero, and the head is positioned at the target track. In FIG. 2, the corresponding current expended to achieve the velocity profile shown in FIG. 4 is displayed. FIG. 3 shows the power consumed in expending the current as shown in FIG. 2.
In FIGS. 5-7, current, cumulative power consumption and velocity profiles graphically illustrate another seek operation in which a coast period is used. As illustrated, the actuator is commanded to accelerate at time T0. This acceleration is held until the actuator reaches maximum velocity VELPK at time TM, where TM is the length of time required to reach maximum velocity. In this example, the maximum velocity VELPK is held (in a xe2x80x9ccoastxe2x80x9d mode) until time TN, at which time the actuator is commanded to decelerate so that the velocity decreases to zero at time TEND.
The velocity profiles illustrated in FIGS. 4 and 7 are idealized profiles in which the head velocity reaches zero at time TEND. It is understood in the art that many variables, including resonant modes of the actuator mechanics and stored energy in the actuator mechanics, prevent a precise correction of actuator velocity which would result in the head landing exactly on track at the conclusion of the seek. These variables may cause the head to overshoot the target track, requiring an extended settling period to position the head within an acceptable range of the target track center.
Disk drives have been designed to operate in a mobile environment. For example, a lap-top computer can be taken from the office or home to a remote location. Because the remote location may or may not have an external power source (e.g., line current), the mobile device is provided with an internal source of power such as, for example, a battery. As used herein, a xe2x80x9cbatteryxe2x80x9d refers to any of a number of sources of D.C. electrical energy which convert chemical energy, nuclear energy, solar energy, thermal energy, or the like, into electrical energy. Unlike external power sources, batteries have a limited amount of available energy, which needs to be conserved in order to extend the operating time of a mobile device between recharging or replacement of batteries. One typical example of an internal power source is a conventional rechargeable battery, such as a lithium-ion battery.
As shown in FIGS. 2 and 5, the servo system draws a significant amount of the available current in seeking target tracks. This results in power consumption that accumulates and can eventually drain the battery. As shown in FIGS. 3 and 6, power is consumed for both acceleration and deceleration operations.
A first aspect of the present invention is a method of performing a seek operation in a disk drive connectable to a mobile device that operates in a mobile environment using battery power and that operates in a docked environment using an external source of power. The disk drive has a spindle motor that rotates a storage medium at an operating angular velocity. The disk drive operates with a servo system that includes a head actuator drive circuit that applies a current to a head actuator to cause the head actuator to move a head to a track of the storage medium and to maintain a position of the head over a selected track of the storage medium. The mobile device provides a command to the disk drive to cause the servo system to perform the seek operation to the selected track. The method comprises the step of receiving an environment signal from the mobile device that indicates whether the mobile device is operating in the docked environment or the mobile environment. The method rotates the storage medium at a same nominal operating angular velocity in the mobile environment and in the docked environment. The method responds to the environment signal and to the command from the host processor to perform one of two alternative steps. The method applies a first set of digital values to the head actuator drive circuit to apply a first current profile to the head actuator to cause the head actuator to move the head to the selected track with a first velocity profile when the environment signal indicates that the mobile device is in the docked environment. The method applies a second set of digital values to the head actuator drive circuit to apply a second current profile to cause the head actuator to move the head to the selected track with a second velocity profile when the environment signal indicates that the mobile device is in the mobile environment.
In accordance with one preferred embodiment of the method, when the method applies the first set of digital values to the head actuator drive circuit to apply the first current profile, the method selects a first acceleration current magnitude and a first acceleration current duration, and when the method applies the second set of digital values to the head actuator drive circuit to apply the second current profile, the method selects a second acceleration current magnitude and a second acceleration current duration. In one particularly preferred embodiment of the method, the second acceleration current magnitude is less than the first acceleration current magnitude. Alternatively, the second acceleration current duration is less than the first acceleration current duration. As a further alternative, the second acceleration current duration is less than the first acceleration current duration, and the second acceleration current magnitude is less than the first acceleration current magnitude.
A second aspect of the present invention is a mobile device that comprises a disk drive and a servo system. The disk drive has a spindle motor that rotates a storage medium at an operating angular velocity, wherein the mobile device operates in a mobile environment using battery power and operates in a docked environment using an external source of power. The servo system has a head actuator drive circuit that applies a current to a head actuator to cause the head actuator to move a head to a selected track of the storage medium. The mobile device comprises an input terminal that receives an environment signal that indicates whether the mobile device is operating in the docked environment or in the mobile environment. A spindle motor controller rotates the storage media at a same nominal operating angular velocity in the mobile environment and in the docked environment. A servo controller is responsive to the environment signal and to a command from the mobile device. The servo controller applies a first set of digital values to the head actuator drive circuit to generate a first current profile to apply to the head actuator to cause the head actuator to move the head to the selected track with a first velocity profile when the environment signal indicates that the mobile device is in the docked environment. The servo controller applies a second set of digital values to the head actuator drive circuit to generate a second current profile to apply to the head actuator to cause the head actuator to move the head to the selected track with a second velocity profile when the environment signal indicates that the mobile device is in the mobile environment.
In accordance with one preferred embodiment of this aspect, the servo controller causes the head actuator drive circuit to generate the first current profile by outputting a first acceleration current magnitude and a first acceleration current duration, and to generate the second current profile by outputting a second acceleration current magnitude and a second acceleration current duration. In one particularly preferred embodiment of this aspect, the second acceleration current magnitude is less than the first acceleration current magnitude. Alternatively, the second acceleration current duration is less than the first acceleration current duration. As a further alternative, the second acceleration current duration is less than the first acceleration current duration, and the second acceleration current magnitude is less than the first acceleration current magnitude.
Another aspect of the present invention is a mobile device that comprises a disk drive and a servo system. The mobile device operates in a mobile environment using battery power and operates in a docked environment using an external source of power. The disk drive includes a spindle motor for rotating a storage medium at an operating angular velocity. The servo system controls the movement of a head actuator in the disk drive. The servo system has a head actuator drive circuit that applies a current to a head actuator to cause the head actuator to move a head to a selected track of the storage medium. The mobile device comprises means for receiving an environment signal that indicates whether the mobile device is operating in the docked environment or the mobile environment. The mobile device further includes means for rotating the storage media at a same nominal operating angular velocity in the mobile environment and in the docked environment. The mobile device further includes means for responding to the environment signal and to the command from the mobile device to perform one of two functions. When the environment signal indicates that the mobile device is in the docked environment, the means for responding applies a first set of digital values to the head actuator drive circuit to apply a first current profile to the head actuator to cause the head actuator to move the head to the selected track with a first velocity profile. When the environment signal indicates that the mobile device is in the mobile environment, the means for responding applies a second set of digital values to the head actuator drive circuit to apply a second current profile to cause the head actuator to move the head to the selected track with a second velocity profile.